Conventional filter apparatus utilized in machine tool operations of the type described in U.S. Pat. Nos. 4,507,061 and RE 32,135 separate machine tool chips and other contaminants from coolant so that clean coolant may be returned to the machine tools for reuse. Often times, the contaminants are very small and of an elongated shape. Usually one or more horizontally disposed filter drums are located adjacent the bottom of a settlement tank. A suction is provided by a pump to the interior of the filter drum to pull coolant through the filter element to move the coolant from one side of the filter to the other. Filter cake, comprised of small chips and other contaminants, is formed on the outside of the drum surface. The drum is periodically indexed to enable a doctor blade to scrape off a portion of the accumulated filter cake, which drops to the bottom of the tank for removal by a dragout conveyor.
The conventional filter element is comprised of a continuous length of wedge shaped wire wrapped around a drum-shaped support. The filter element thereby includes elongated openings through which some elongated contaminants are allowed to pass if the contaminants are aligned in the direction of fluid movement as they strike the filter. The passage of these elongate contaminants allows the contaminants that pass through the filter to be recirculated to the machine tools.
An alternate type filter system that has been tried is fabricated from rectilinear mesh, wire cloth or the like. Although the minute square openings formed by the woven wire cloth are effective in preventing the passage of elongate contaminants, the surface is not a flat planar surface and thus becomes clogged when scrape cleaning is attempted.
In drum-type filters, a thin screen element or microscreen with tiny perforations therethrough are often mounted on a drum-shaped support cylinder. The support cylinder has moderately sized holes. Fluid filters through the perforations in the screen element and then through the holes of the support cylinder to reach the interior of the filter drum.
The screen element often begins as planar rectangular sheet. The sheet is pulled taut about the support cylinder and then ends of the sheet are joined to form a seam holding the screen element tautly about the support cylinder. However, when the seam is repeatedly scraped by doctor blades, the screen element can become worn and tear. Also, the screen element can often be manufactured more inexpensively as an endless cylinder or tube as compared to starting with a planar sheet and then joining ends together to form a closed cylinder or tube with a seam.
Disc filter elements may comprise many components. First, a central frame is provided to support the disc filter element. Next, screen support structures often are sandwiched about the central frame. Perforated screen elements are placed over the screen support structures. Finally, these components are joined together by a retainer.
The screen support structures are important in that they provide support to screen elements to prevent the screen elements from becoming overstressed and tearing while still allowing for proper fluid flow through the disc filter element. This is particularly true for very thin screen elements. However, by increasing the number of components in the disc filter element, such as by adding screen support structures, the cost and complexity of making the disc filter element also increases. Further, the filter support structures can become a serious impediment to fluid flow if not properly designed.
Therefore, there is a need for a simple, inexpensive disc filter element which can be used with thin screen elements and which has relatively few parts while providing adequate support to the screen elements.